“Yes. You see? They laboured to preserve life — us, Bobby — even in the midst of the greatest catastrophe the planet has suffered.

“And that is our destiny, Bobby. Just as the Sisyphans preserved their handful of thermophilic microbes to outlive the impact — just as those algal mats and seaweed struggled to outlast the savage glaciation episodes, just as complex life, evolving and adapting, survived the later catastrophes of volcanism and impact and geological accident — so must we. Even the Joined, the new evolution of mind, are part of a single thread which reaches back to the dawn of life itself.”

Bobby smiled. “Remember what Hiram used to say? ‘There’s no limit to what we can achieve, if we work together.’ ”

“Yes. That’s it exactly. Hiram was no fool.”

Fondly, Bobby touched his brother’s shoulder. “I think -”

— and, once again, without warning, the world imploded into darkness.

“Bobby. Please wake up, Bobby. Can you hear… me?…”

The voice came to him, as if from afar. A woman’s voice. He heard the voice, understood the words, even before a sense of his body returned.

His eyes were closed.

He was lying flat on his back on what felt like a deep, soft bed. He could feel his limbs, the slow pulse of his heart, the swell of his breath. Everything seemed normal. And yet he knew it was not. Something was wrong, as subtly askew as the violet sky of the Cretaceous.

He felt unaccountably afraid.

He opened his eyes.

A woman’s face hovered before him — fine-boned, blue-eyed, blond hair, some lines at the eyes. She might have been forty, even fifty. Yet he recognized her.

“…Mary?”

Was it his voice?

He raised his hand. A bony wrist protruded from a sleeve of some silvery fabric. The hand was fine-boned, the fingers narrow and long, like a pianist’s.

Was it his hand?

Mary — if it was Mary — leaned forward and cupped his face. “You’re awake. Thank Hiram for that. Can you understand me?”

“Yes. Yes, I…”

“What do you remember?”

“David. The Wormworks. We were…”

“Travelling. Yes. Good; you remember. On his Anastasis David told us what you had seen.”

Anastasis. he thought. Resurrection. His fear deepened.

He tried to sit up. She helped him. He felt weak, light.

He was in a smooth-walled chamber. It was dark. A doorway led to a corridor, flooded with light. There was a single small window, circular. It revealed a slab of blue and black.

Blue Earth. Black sky.

The air of Earth was clear as glass. There was a silver tracery over the blue oceans, some kind of structure, hundreds of kilometres above the surface. Was he in orbit? No, the Earth was not turning. He was in some kind of orbital tower, then.

My God, he thought.

“Am I dead? Have I been resurrected, Mary?”

She growled, and ran her hand through loose hair. “David said you’d be like this. Questions, questions.” Her intonation was clumsy, her voice dry, as if she wasn’t used to speaking aloud.

“Why have I been brought back?… Oh. The Wormwood. Is that it?”

Mary frowned, and briefly seemed to be listening to remote voices. “The Wormwood? You mean the comet. We pushed that away long ago.” She said it casually, as if a moth had been brushed aside.

Bemused, he asked, “Then what?”

“I can tell you how you got here,” she said gently. “As to why, you’ll have to figure that out for yourself…”

Sixty more years had worn away, he learned.

It was the WormCam, of course. It was possible now to look back into time and read off a complete DNA sequence from any moment in an individual’s life. And it was possible to download a copy of that person’s mind — making her briefly Joined, across years, even decades — and, by putting the two together, regenerated body and downloaded mind, to restore her.

To bring her back from the dead.

“You were dying,” said Mary. “At the instant we copied you. Though you didn’t know it yet.”

“My cloning.”

“Yes. The procedure was still experimental in Hiram’s time. There were problems with your telomeres.” Genetic structures that controlled the ageing of cells. “Your decline was rapid after…”

“After my last memory, in the Wormworks.”

“Yes.”

How strange to think that even as he handed that last cup of coffee to David his life had already been effectively over, the remnant, evidently, not worth living.

She took his hand. When he stood, he felt light, dream-like, spindly. For the first time he noticed she was naked, but wearing a pattern of implants in the flesh of her arms and belly. Her breasts seemed to move oddly: languidly, as if the gravity wasn’t quite right here.

She said, “There is so much you must learn. We have room now. The Earth’s population is stable. We live on Mars, the moons of the outer planets, and we’re heading for the stars. There have even been experiments in downloading human minds into the quantum foam.”

“Room for what?”

“For the Anastasis. We intend to restore all human souls, back to the beginning of the species. Every refugee, every aborted child. We intend to put right the past, to defeat the awful tragedy of death in a universe that may last tens of billions of years.”

How wonderful, he thought. A hundred billion souls, restored like the leaves of an autumnal tree. What will it be like?

“But,” he said slowly, “are they the same people? Am I me?”

“Some philosophers argue that it’s possible. Leibniz’s Identity of the Indiscernibles tells us that you are you. But…”

“But you don’t think so.”

“No. I’m sorry.”

He thought that over.

“When we’re all revived, what will we do next?”

She seemed puzzled by the question. “Why — anything we want, of course.” She took his hand. “Come. Kate is waiting for you.”

Hand in hand they walked into the light.

The concept of a “time viewer,” though venerable, has been explored only sparingly in science fiction — perhaps because it is so much less dramatic than time travel. But there have been a number of remarkable works on the theme, ranging from Gardner Hunting’s The Vicarion (1926) to Orson Scott Card’s Pastwatch: The Redemption of Christopher Columbus (1996). One of us has briefly sketched its implications in previous works (Childhood’s End, 1953, “The Parasite,” 1953). Perhaps the best-known and best-example is Bob Shaw’s “slow glass” classic which shares our title (Analog, August 1966).

Today the notion has the first glimmers of scientific plausibility, offered by modern physics — and a resonance with our own times, surrounded as we are increasingly by the apparatus of surveillance.

The concept of spacetime wormholes is well described in Kip Thorne’s Black Holes and Time Warps: Einstein’s Outrageous Legacy (W. W. Norton, 1994). The proposal that wormholes might be generated by “squeezing the vacuum” was set out by David Hochberg and Thomas Kephart (Physics Letters B, vol. 268, pp. 377-383, 1991).

The very speculative and, we hope, respectful reconstruction of the historical life of Jesus Christ is largely drawn from A. N. Wilson’s fine biography Jesus (Sinclair-Stevenson, 1992). For assistance with the passages on Abraham Lincoln the authors are indebted to Warren Allen Smith, New York correspondent of Gay and Lesbian Humanist (UK).

The idea that primitive Earth was afflicted by savage glacial episodes has been proposed by Paul Hoffman of Harvard University and his coworkers (see Science, vol. 281, p. 1342, 28 August 1998). And the notion that primitive life might have survived Earth’s early bombardment by sheltering deep underground is explored, for example, in Paul Davies’ The Fifth Miracle (Penguin, 1998).